This invention relates to the synthesis of aluminophosphate and silicoaluminophosphate molecular sieves of the CHA framework type. In particular the present invention relates to the synthesis of aluminophosphate and silicoaluminophosphate molecular sieves of the CHA framework type using synthesis templates that contain two dimethylamino moieties in combination with hydrogen fluoride.
Olefins are traditionally produced from petroleum feedstock by catalytic or steam cracking processes. These cracking processes, especially steam cracking, produce light olefin(s) such as ethylene and/or propylene from a variety of hydrocarbon feedstock. It has been known for some time that oxygenates, especially alcohols, e.g. methanol, are convertible into light olefin(s). The preferred methanol conversion process is generally referred to as methanol-to-olefin(s) (MTO) process, where methanol is converted to primarily ethylene and propylene in the presence of a molecular sieve.
Some of the most useful molecular sieves for converting methanol to olefin(s) are the metalloalluminophosphates such as the silicoaluminophosphates (SAPO""s). There are a wide variety of SAPO molecular sieves known in the art, of these the more important examples include SAPO-5, SAPO-11, SAPO-18, SAPO-34, SAPO-35, SAPO-41, and SAPO-56. For the methanol-to-olefins process SAPO molecular sieves having the CHA framework type (xe2x80x9cAtlas of Zeolite Framework Typesxe2x80x9d, 2001, 5th Edition, p. 96) and especially SAPO-34 are particularly important catalysts. The CHA framework type has a double six-ring structure in an ABC stacking arrangement. The pore openings of the structure are defined by eight member rings that have a diameter of about 4.0 xc3x85, and cylindrical cages within the structure of approximately 10xc3x976.7 xc3x85. Other SAPO molecular sieves of CHA framework type include SAPO-44, SAPO-47 and ZYT-6.
The synthesis of AlPO4 and SAPO molecular sieves is a complicated process. There are a number of variables, which need to be controlled in order to optimise the synthesis in terms of the purity, yield, and quality of the molecular sieve produced. Of these variables the choice of synthesis template is usually one of the most important in determining which framework type is obtained.
One desirable group of silicoaluminophosphate molecular sieves are those, which have low silicon contents. Silicoaluminophosphates of the CHA framework type with low silicon contents are particularly desirable for use in the methanol-to-olefins process. Wilson, et al., reported that it is beneficial to have lower Si content for methanol-to-olefins reaction (Microporous and Mesoporous Materials, 29, 117-126, 1999). Low Si content has the effect of reducing propane formation and decreasing catalyst deactivation.
In U.S. Pat. No. 4,440,871 (Lok et al.) the synthesis of a wide variety of SAPO materials of various framework types are described with a number of specific examples. Also disclosed are a large number of possible organic templates, with some specific examples. In the specific examples a number of CHA framework type materials are described. SAPO-34 is prepared utilising tetraethylammonium hydroxide (TEAOH), or isopropylamine, or mixtures of TEAOH and dipropylamine (DPA). This is believed to be the first reported synthesis of a SAPO-34 of CHA framework type. Also disclosed in this patent is a specific example that utilises cyclohexylamine in the preparation of SAPO-44. Although other template materials are described in this patent there are no other templates indicated as being suitable for preparing SAPO""s of CHA framework type. Certain aminoalcohols are mentioned, including triethanolamine, N-methyldiethanolamine, N-methylethanolamine, N,N-dimethylethanolamine and N,N-diethylethanolamine as possible templates for SAPO molecular sieves. Of these materials N,N-diethylethanolamine is shown to produce SAPO-5, which is of framework type AFI. For the other aminoalcohols no indication is provided as to which SAPO or which framework type may be obtained through their use.
Since the synthesis of SAPO-34 was reported in U.S. Pat. No. 4,440,871, tetraethylammonium hydroxide (TEAOH) either alone, or in combination with dipropyl amine (DPA), has been the template of choice for preparing SAPO-34. However, there are problems associated with the use of TEAOH and DPA. When used alone, TEAOH affords a limited range of synthesis parameters. For example, under certain conditions TEAOH will also template the synthesis of SAPO-18, which has the AEI framework type. TEAOH is thus relatively intolerant to synthesis condition variations. TEAOH is sometimes combined with DPA. However, DPA has a low boiling point (110xc2x0 C.) resulting in the need for production plants that can handle high pressures. In certain countries, the use of DPA requires special regulatory authorizations due to its toxicity. Also, DPA is an aggressive template and is often implicated in re-dissolution of the silicoaluminophosphate molecular sieve during its synthesis, resulting in poor quality crystalline product due to surface pitting of the crystals. Finally, it has proved difficult up to now to make pure phase CHA silicoaluminophosphate molecular sieves with low silica to alumina ratio. Although there are problems associated with TEAOH and DPA, no completely satisfactory alternative template materials have been reported yet for the preparation of silicoaluminophosphate molecular sieves with the CHA framework type. A further problem associated with the use of TEAOH is that silicoaluminophosphate molecular sieves with the CHA framework produced using this template are relatively expensive due to long crystallization times that are typically between 24 to 72 hours. In a Ph.D. thesis (E. H. Halvorsen, University of Oslo, 1996), it was reported that low silica SAPO-34, designated as UiO-S4, was produced using TEAOH template in combination with HF. When TEAOH is used in combination with hydrogen fluoride the crystallization times may be reduced to between 16 to 24 hours; whilst this is an improvement the resultant molecular sieves are still expensive.
In U.S. Pat. No. 4,440,871, it was reported that SAPO-44 was obtained xe2x80x9cas the major phasexe2x80x9d using cyclohexylamine as template. In U.S. Pat. No. 6,162,415 (Liu, et al.), relatively pure CHA SAPO-44 was obtained using the same template but with control of the ratio of template to aluminium component and the ratio of phosphorous component to aluminium component. In European Patent Publication No. 0,993,867, it was reported that the use of methylbutylamine resulted in SAPO-47 and the use of cyclohexylamine resulted in impure SAPO-44. Methylbutylamine has an even lower boiling point, at 91xc2x0 C., than DPA.
When attempts have been made to utilise other types of template compounds such as aminoalcohols, silicoaluminophosphates of framework type other than CHA have been obtained. In U.S. Pat. No. 4,861,739 (Pellet, et al.), Example 102, it was reported that the use of N,N-diethylethanolamine produced CoAPSO-47, having Si concentrated on the peripheries of the crystal and Co at the centre. In U.S. Pat. No. 4,310,440 (Wilson et al.), triethanolamine, N,N-dimethylethanolamine, N,N-diethylethanolamine, N-methyldiethanolamine, and N-methylethanolamine, were all used to prepare AlPO4-5, aluminophosphates of framework type AFI. N-methylethanolamine was also reported to produce AlPO4-21 of framework type AWO. In European Patent Publication No. 0,993,867, it was reported that diethanolamine produced SAPO-34 and SAPO-5 under different synthesis conditions. To-date all attempts to reproduce this SAPO-34 synthesis have failed.
In the art various attempts have been made to improve the synthesis of AlPO4 or SAPO molecular sieves. One approach has been the use of fluoride addition to the synthesis. In U.S. Pat. No. 5,096,684 (Guth et al.), morpholine and tetraethylammonium hydroxide were found to template the production of SAPO-34 when in the presence of HF. According to Guth et al., the use of HF in combination with the organic template results in silicoaluminophosphates which have improved thermal and hydrolytic stability. No other templates were found to produce silicoaluminophosphates of CHA framework type in the presence of fluoride ions, although various other templates were found to produce many other framework types in the presence of HF. H. Kessler et al. (H. Kessler, J. Patarin and C. Scott-Darie, Studies in Surface Science and Catalysis, Vol. 85 (1994), pp. 75-113) refers to the work of M. Goepper (Ph. D. Thesis of M. Goepper, Universitxc3xa9 Haute Alsace, Mulhouse (France), 1990). In her thesis, M. Goepper reports crystallization of an aluminophosphate of CHA framework from heating for 24 hours at 200xc2x0 C. a synthesis mixture having the composition 1.0HF:1.5TMED:Al2O3:P2O5:80H2O. M. Goepper reports that this CHA phase was not obtained when a source of divalent metal was added to the synthesis mixture. In the absence of HF and in the absence of a source of divalent metal, the formation of AlPO4-21 is reported with TMED as template. In U.S. Pat. No. 4,786,487 (Kuehl), SAPO-20 was produced from synthesis mixtures containing tetramethylammonium hydroxide and fluoride ions from water-soluble sources of fluoride such as Na, K and ammonium fluoride. In U.S. Pat. No. 6,001,328 (Lillerud et al.), silicoaluminophosphate indicated as UiO-S7 was prepared using tetramethylammonium hydroxide pentahydrate or tetramethylammonium hydroxide, in combination with HF. In a Ph.D. thesis (E. H. Halvorsen, University of Oslo, 1996), it was reported that low silica SAPO-34, designated as UiO-S4, was produced using TEAOH template in combination with HF.
In the art various attempts have been made to synthesis of AlPO4 or SAPO molecular sieves using templates based on the alkylene diamine or polyamine structures such as for example those based on for example ethylenediamine, 1,3-propanediamine, and 1,6-hexanediamine.
In European Patent Publication No. 0,043,562, it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine as organic template resulted in the formation of AlPO4-21. In European Patent Publication No. 0,538,958, it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine as organic template resulted in the formation of an AlPO4 referred to as SCS-24. In European Patent Publication No. 1,142,833, it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of MeAPSO-56 and SAPO-56. In U.S. Pat. No. 4,898,660 (Wilson et al.), ethylenediamine was used to prepare AlPO4-12. N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-propane-1,3-diamine and N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine were reported to produce AlPO4-21. In U.S. Pat. No. 5,370,851 (Wilson), it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56. In U.S. Pat. No. 5,232,683 (Clark et al.), it was reported that the use of 1,8-diaminooctane and 1,10-diaminodecane as organic templates resulted in the formation SAPO""s and CoAlPO""s of type SCS-22. Wilson, et al., have reported the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of AlPO-17, SAPO-17, MAPSO-34 and SAPO-56 (Microporous and Mesoporous Materials, 28(1), 117-126, 1999 and Studies in Surface Science and Catalysis (1995) 98, (Zeolite Science 1994: Recent Progress and Discussions), 9-10). Bu, et al., have reported the use of, N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine and 1,3-diaminopropane as structure directing agents for the formation of cobalt aluminophosphates UCSB-4 and UCSB-5 (Microporous and Mesoporous Materials, 25(1-3), 109-117,1998).
Feng, et al., have reported that a variety of cobalt phosphates having zeolite like structures could be prepared using a variety of alkylene diamines as structure directing agents (Nature (London), 388(6644), 735-741,1997). In a latter work it was reported that cobalt aluminophosphates of CHA framework type could be prepared using N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template and a zinc aluminophosphate of CHA framework type could be prepared using N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,3-butanediamine as organic template (Microporous and Mesoporous Materials, 23, 221-229,1998). Ferey, et al., have reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template in the presence of ammonium fluoride produced AlPO-CJ2 (Journal of Solid State Chemistry 105(1), 179-90, 1993). Long, et al., have reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine as organic template resulted in the formation of an AlPO4-21 and an AlPO4 molecular sieve named CFAP-2 (Chemical Journal of Chinese Universities 7(2), 100-4, 1986 and Journal of Fudan University (Natural Science) 25(3), 301-8, 1986). Tian, et al., have reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56 and MAPSO-56 molecular sieves (Studies in Surface Science and Catalysis (2001), 135 (Zeolites and Mesoporous Materials at the Dawn of the 21st Century), 891-898 and Chemical Journal of Chinese Universities 22(6), 991-994,2001).
In Chinese Patent No. 1,299,776, it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56 molecular sieve. In Chinese Patent No. 1,301,598, it was reported that the use of N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl-1,6-hexanediamine as organic template resulted in the formation of SAPO-56, and various MeAPSO-56 molecular sieves.
As can be seen from the disclosures described herein, there have been a number of attempts to find alternative synthesis templates for the CHA framework type with limited success. It is desirable therefore to find new synthesis templates and template systems that are specific for the synthesis of silicoaluminophosphate molecular sieves having the CHA framework type. In addition there is a need for new templating systems which afford more effective control of the final composition of the SAPO molecular sieve materials and in particular the Si content of the final product. In addition a further need is to obtain SAPO materials having the CHA framework type that have a low acid density, which is normally directly related to low silica content. A further desire is to find methods of reducing the crystallization times for the synthesis of aluminophosphate and silicoaluminophosphate.
The present invention provides a process for preparing microporous crystalline silicoaluminophosphate molecular sieves of CHA framework type, the process comprising:
(a) providing a reaction mixture comprising a source of alumina, a source of phosphate, a source of silica, hydrogen fluoride and an organic template comprising one or more compounds of formula (I):
(CH3)2Nxe2x80x94Rxe2x80x94N(CH3)2xe2x80x83xe2x80x83(I) 
xe2x80x83wherein R is an alkyl radical of from 1 to 12 carbon atoms;
(b) inducing crystallization of silicoaluminophosphate from the reaction mixture; and
(c) recovering silicoaluminophosphate molecular sieve.
In one embodiment of the present invention there is provided a silicoaluminophosphate molecular sieve, substantially of CHA framework type, comprising within its intra-crystalline structure fluoride and at least one template of the formula (I)
(CH3)2Nxe2x80x94Rxe2x80x94N(CH3)2xe2x80x83xe2x80x83(I) 
wherein R is an alkyl radical of from 1 to 12 carbon atoms.
In another embodiment, the present invention provides a process for preparing microporous crystalline aluminophosphate molecular sieves of CHA framework type, the process comprising:
(a) providing a reaction mixture comprising a source of alumina, a source of phosphate, hydrogen fluoride and an organic template comprising one or more compounds of formula (Ixe2x80x2):
(CH3)2Nxe2x80x94Rxe2x80x94N(CH3)2xe2x80x83xe2x80x83(Ixe2x80x2) 
xe2x80x83wherein R is an alkyl radical of from 3 to 12 carbon atoms;
(b) inducing crystallization of aluminophosphate from the reaction mixture; and
(c) recovering aluminophosphate molecular sieve.
In another embodiment of the present invention there is provided a composition of a microporous crystalline silicoaluminophosphate molecular sieve, which has a characteristic X-ray powder diffraction pattern containing at least the d-spacings as set forth in Table A:
It is preferred that the composition as identified in Table A comprises N,N,Nxe2x80x2,Nxe2x80x2-tetramethyl ethylenediamine and fluoride within its intra-crystalline structure.
In another embodiment the present invention provides a method for the manufacture of a formulated catalyst composition, which method comprises forming a mixture comprising at least one microporous crystalline silicoaluminophosphate molecular sieve of CHA framework type comprising within its intra-crystalline structure fluoride and at least one template which contains one or more compounds of general formula (I) wherein R is an alkyl radical of from 1 to 12 carbon atoms or as obtained from a process utilising a template comprising one or more compounds of the formula (I) wherein R is an alkyl radical of from 1 to 12 carbon atoms, in combination with hydrogen fluoride, with at least one formulating agent, to form a catalyst composition.
In yet a further embodiment the present invention provides for a formulated molecular sieve composition comprising at least one microporous crystalline silicoaluminophosphate molecular sieve of CHA framework type comprising within its intra-crystalline structure fluoride and one or more compounds of general formula (I) wherein R is an alkyl radical of from 1 to 12 carbon atoms or as obtained from a process utilising a template comprising one or more compounds of general formula (I) wherein R is an alkyl radical of from 1 to 12 carbon atoms, in combination with hydrogen fluoride, in admixture with at least one formulating agent.
In a further embodiment the present invention provides for the use of a template comprising one or more compounds of general formula (I) wherein R is an alkyl radical of from 1 to 12 carbon atoms in combination with hydrogen fluoride ions in the synthesis of silicoaluminophosphates of CHA framework type.
In yet a further embodiment, the present invention provides for the use of a template comprising one or more compounds of general formula (Ixe2x80x2) wherein R is an alkyl radical of from 3 to 12 carbon atoms in combination with hydrogen fluoride ions in the synthesis of aluminophosphates of CHA framework type.